A solar thermal power system based on Direct Steam Central Receiver (DSCR) includes a large field of heliostats and a solar receiver placed on a tower of substantial height. The heliostats focus direct sunlight on to the solar receiver to produce steam to be utilized to run a steam turbine from producing electricity. Typically, the solar thermal power plant operates on a daily cycle, during clear sunlight hours, while shutting down in nights or in cloudy seasons. However, if the solar thermal power plant is to meet increasing electricity demand, it needs to be operable irrespective of the availability of solar light, i.e., in nights or in cloudy days. A realization of such a solar thermal power plant generates a requirement of storing solar thermal energy during day times and use in nights or in cloudy days. For meeting such requirements, a central receiver including a solar energy storage fluid, such as molten salt, is generally used. The central receiver with molten salt is generally known as Molten Salt Central Receiver (MSCR).
A typical MSCR system 10 is evident in FIG. 1. The MSCR system 10 includes a MSCR 12, hot and cold storage tanks 14, 16 and a Molten Salt Steam Generator (MSSG) cycle 18. The molten salt fluid heated at the MSCR 12 is stored in the hot storage tank 14, at a temperature of about 550° C. to 600° C. After thermal energy thereof is utilized by the MSSG cycle 18 to generate power by a power generation cycle 20 having turbines and generator set 22, it is stored in the cold storage tank 16, at a temperature of about 290° C., from where it is further sent to the MSCR 12 for reheating. In FIG. 1, a dotted line depicts a molten salt flow circuit.
In such MSCR systems, the temperature of the molten salt is required to be maintained at a specific temperature of about 550° C. to 600° C. Specifically, such temperature of the molten salt is required to be maintained at the outlet of the MSCR 12 in order to maximize efficiency while avoiding degradation of the molten salt by overheating.
Conventionally, such temperature is controlled either by adjusting solar heat flux applied to the MSCR 12 surface or by adjusting the molten salt flow through the MSCR 12. Both of these methods may be relatively slow and inefficient to provide proper control of the temperature due to the presence of inherently dynamic solar Daily Normal Irradiance (DNI).
Accordingly, there exists a need for an alternate provision in order to get a relatively faster response and consequently improved control performance of the relatively hot molten salt temperature at the outlet of the MSCR.